The present invention relates to a method for checking the positioning accuracy of a machine part that is displaceable with respect to at least one axis by means of a drive and a controller, wherein the machine part is displaced only with respect to the one axis in that the controller specifies nominal position values of the machine part in relation to the one axis.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Among the methods known for checking the positioning accuracy of a CNC machine tool is the so-called circular test. With the circular test, at least two axes of the machine tool are controlled in such a way the tool center point (TCP) describes a circular path. In particular, the two axes are moved jointly by way of a circular interpolation. The circular interpolation generates a sine motion profile for one machine axis and a cosine motion profile for the other. The real actual position values of the tool center point are acquired by means of a measurement system and presented graphically in a circular representation. In order to enable the deviations of the real circular path from the likewise depicted ideal circular path to be more readily recognized, it is common practice to represent the deviations with respect to the ideal circular path in greatly magnified form. For the deviations in relation to the ideal circular path, a different scale is accordingly used, in particular a greatly magnified scale compared to the ideal circular path. Mechanical and dynamic errors of machine axes can be determined by means of the circular test.
The following problems occur with the cited approach:
a) Generally, not every machine axis can be interpolated in the circle together with every other one, which makes checking the positioning accuracy more difficult for such axes.
b) With different dynamic settings in the axes interpolating with one another, the influence of the different axis dynamics dominates the circular test and consequently the circular representation to such an extreme extent that the more minor mechanical contour errors that are caused e.g. due to friction or mechanical backlash are no longer recognizable as deviations in the circular representation.
c) When two machine axes that are mechanically coupled to one another are interpolated, it is not always possible—due to the mutual mechanical influence—for the contour errors detected in the machine axes to be assigned unequivocally to one of the two machine axes.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method for checking the positioning accuracy in which the cited problems do not occur.